Nuclear fission

Summary

This document provides guidance in the implementation of external events modeling in extended L2 PSA and is a complement of the ASAMPSA2 guidelines in this area. The conclusions of the ASAMPSA_E end-users survey and of technical meetings of WP10, WP21, WP22, and WP30 at Vienna University in September 2014 which are relevant for L2 PSA have been reflected in the content of the present document and are being taken into account as much as it is possible with the current status of knowledge.

Issues that belong only to Level 1 PSA analyses in general are not discussed, and it is assumed that the only relevant issues to be resolved according to the end-users’ wish list are those subsequent to core damage and/or fuel degradation, i.e. after permanent loss of core cooling and/or decay heat removal functions. Following the accident at Fukushima Dai-ichi, the nuclear safety community has realized that much attention should be given to the areas of operator interventions and accidents that may develop at the same time in more than one unit if they are initiated by one or more common external events. For this reason and to fulfill the PSA end-users’ wish list, the attention is mostly focused on interface between Level 1 and Level 2, human response analysis and some consideration is given to Level 2 modeling of severe accidents for multiple unit sites, even though it is premature to provide extensive guidance in this area.

ASAMPSA_E Partners

The following table provides the list of the ASAMPSA_E partners involved in the development of this document.

1	Institute for Radiological Protection and Nuclear Safety	IRSN	France
2	Gesellschaft für Anlagen- und Reaktorsicherheit mbH	GRS	Germany
8	Cazzoli Consulting	CCA	Switzerland
9	Italian National Agency for New Technologies, Energy and the Sustainable Economic Development	ENEA	Italy
14	NUBIKI	NUBIKI	Hungary
24	Jožef Stefan Institute	JSI	Slovenia
27	Technical University of Sofia – Research and Development Sector	TUS	Bulgaria

Table of content

Change history 5

List of diffusion 6

Summary 10

ASAMPSA_E Partners 11

Table of content 12

List of Tables 12

List of Figures 13

Glossary 14

1Introduction 15

1.1External events under consideration 15

1.2Impact of external events on L2 PSA issues 16

2External events specific issue impacting L2 PSA 16

2.1Definition of Plant Damage States (PDS) 16

2.2Containment Analysis, Phenomena and Source Terms 19

2.2.1General considerations 19

2.2.2Examples 20

2.3Human reliability analysis 23

2.3.1General considerations 23

2.3.2HRA shaping factors 25

2.4Event tree modelling 27

2.5Quantification of Event trees 28

2.6Defence-In-Depth under external events loads 30

2.7Analysis and presentation of results 31

2.7.1L2 PSA results and harmonization 32

2.7.2Analysis of results 34

2.7.3Presentation of results 35

2.8Issues involving multi units sites 35

2.8.1General considerations 35

2.8.2Proposal for multi-unit site analysis 40

3Compliance with end-user’s needs 43

4Conclusions 44

5Recommendations 46

6List of references 47

7Appendix 50

7.1Appendix 1 - Example of an on-going seismic fragility analysis at IRSN (main steam line of a PWR) 50

7.2Appendix 2 - Compliance of the report with the PSA End-Users Needs 53

List of Tables

List of Figures

Not Applicable

Glossary

ACWS	Auxiliary Cooling Water System
AESJ	Atomic Energy Society of Japan
APET	Accident Progression Event Tree
BWR	Boiling Water Reactor
DiD	Defence in Depth
CCF	Common Cause Failure
CD	Core Damage
CDF	Core Damage Frequency
CDS	Core Damage State
CRT	Common Risk Target
ENSI	Eidgenössisches Nuklearsicherheitsinspektorat (Swiss Federal Nuclear Safety Inspectorate)
EOP	Emergency Operating Procedure
FCI	Fuel Coolant Interaction
FCVS	Filtered Containment Venting System
FP	Fire Protection
HRA	Human Reliability Analysis
L1	Level 1
L2	Level 2
MCCI	Molten Core Concrete Interaction
MCS	Minimal Cut-Set
PDS	Plant Damage State
PSA	Probabilistic Safety Analysis
RCS	Reactor Coolant System
SAM	Severe Accident Management
SAMG	Severe Accident Management Guidelines
SFP	Spent Fuel Pool
SSC	Structures, Systems and Components